Transformer



Oct. 22, 1929. L, H, HILL 1,132,719

TRANSFQRMER Filed Aug. 30,1923

INVENTOR Le/anahCHi/A I ATTORNEY Patented Oct. 22, 1929" UNITED STATES PATENT OFFICE LELAND H. HILL, OF WILKINSBURG, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE I ELECTRIC 8a MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA TRANSFORMER Application filed August 30, 1923. Serial No. 680,115.

My invention relates to transformers and it has particular relation to transformers of the type provided with an overflow tank.

One object of my invention is to provide means whereby a body of inert gas may be maintained in contact with the insulating fluid of transformers.

A second object of my invention is to provide means whereby the breathing or exchange of air between transformers and the atmosphere is materially reduced.

A further object of my invention is to provide means whereby the insulating fluid of transformers of the overflow type is maintained out of contact with an oxidizing atmosphere.

In the operation of transformers, circuit breakers, or the like, it has been found that explosive mixtures are formed by the volatilization of the insulating oil, or the breaking down of the latter incident to electrical arcs that occur under-the surface of the oil as a result ofshort circuits or other abnormal conditions. It has been found, further, that the quality of the insulating oil deteriorates in the presence of ordinary air by reason of the oxidation of the oil to form sludge. .The insulating properties of the oil are further diminished by the-tendency of the oil to absorb a certain percentage of air.

In accordance with the present invention, I provide an expansion or overflow tank that is connected to the main tank below the'level of the insulating oil. Deoxidizing materialoccupies a compartment that com municates with the space above the oil in the transformer tank. The overflow tank is connected to the atmosphere through a respie rator or deoxidizing apparatus for removing oxygen from such air as may enter the.

overflow tank during the breathing of the transformer.

In the accompanying drawing,

Figure 1 is a view, partially in elevation and partially in section, of a transformer constructed in accordance with my invention' Fig. 2 is a view in transverse section taken along the line 11-11 of Fig. 1.

A transformer 1 comprises a tank 2 that is partially filled with oil indicated at 3. The tank 2 is provided with a cover member 4, from which the terminals of the windings are insulated by means of suitable bushings 5 and 6. The space 7 above the oil 3 is initially filled with ordinary air.

An expansion overflow tank 9, which may be supported in any suitable manner, is con nected at its lower portion to the tank 2 below'the level of the oil by means of pipes 10 and 11. The upper portion of the overflow tank 9 is connected by means of a pipe 12 to a deoxidizing apparatus, or respirator 13.

The respirator 13 comprises an enclosing casing 14, a container 15 for deoxidizing material which vmay be of any suitable character, but is preferably that constituting the subject matter of the copending application of C. J. Rodman and A. H, Maude, Serial No. 652,668, filed July 20, 1923, and assigned to the \Vestinghouse Electric and Manufacturing Company. The container 15 is preferably constructed of woven or sheet material, having perforations and is sealed at its edges to the walls of the casing 14. The

details of construction of the respirator 13 are similar to those constituting the subject matter of the copending application of C. J. Rodman and L. H. Hill, Serial No. 660,116, filed Aug. 30, 1923, and assigned to the Westinghouse Electric and Manufacturing Company.

The upper portion of the respirator 13 is sealed from the lower portion by means of a partition 17, or separate casings may be provided, if desired. The upper compartment thus formed communicates with the space 7 by means of an opening 18. The deoxidizing material in the portion of the container 15 in the upper compartment is accordingly effective to deoxidize the air or gas in the space 7. a

The lower compartment of the respirator, which is connected to the upper portion of the overflow tank 9 on one side of the container 15, is connected on the other side of the container to the atmosphere by means of a valve 19. The valve 19, which is here represented as a U-tube of conventional form containing mercury, or other suitable liquid, to constitute a seal, is preferably replaced in practice by the valve constituting the subject matter of my copending application, Serial No. 608,791, filed December 23, 1922.

It may be assumed that the transformer and its associated parts are substantially at room temperature and that the level of the oil in the tank 2 is approximately that indicated in the drawing. The level of the oil in the pipe 10 will accordingly be substantially the same. It may be assumed further that the transformer is being placed in operation and that its temperature is increasing by reason of the heat losses of the windings of the transformer.

The rising temperature causes an increase in the volume of oil 3 with a corresponding increase in the pressure applied to the air or gas in the space 7. The increased pressure within the tank 2 causes the oil to rise in the pipe 10 and into the overflow tank 9 until the pressure in the tank 9 and the head of the oil in the tank 9 and the pipe 10 equal the pressure in the space 7 and the head of oil in the main tank applied to the pipe 10. The entrance of oil into the overflow tank 9 causes an increase in the pressure of the air or gas therein that is transmitted to-the respirator 13 and the Valve 19. -When the pressure reaches a predetermined maximum, that is determined by the adjustment of the valve 19, air escapes from the tank 9 through the pipe 12, respirator 13 and valve 19 to the atmosphere. This release of air occurs at each successive increase in value of the pressure in the overflow tank to the predetermined maximum.

Incase the temperature of the oil decreases by reason of changes in load conditions, or

or other. reasons, the pressure within the main tank falls and, accordingly, oil is returned from the overflow tank to the main tank. This action results in a decrease in pressure in the auxiliary tank 9 and when the pressure therein is below atmospheric pressure, to such degree that the valve 19 opens, air enters the respirator 13, traverses deoxidizing material 15,is deoxidized thereby andsubstantially pure nitrogen enters the overflow tank 9. The valve '19 closes as soon as the pressure is substantially equalized and remains closed until the difference in-pressure again reaches the one or the other predetermined value. B wa of example, the valve mechanism may e a justed to permit gas to be expelled from the tank 9 when the pressure is five pounds 'per square inch above atmospheric pressure and to permit air to be admitted when the pressure is one-fourth of one pound per square inch below atmospheric pressure.

The volume of gas .or deoxidized air within the space 7 remains substantially constant unless the level of the oil 3 falls below the entrance to the pipe 11, or the pressure in the main tank is less than that in the expansion tank, b an amount equal to the head of oil above the pipe 11 in the main tank. In such cases, inert gas is drawn into the main tank 7 from the overflow tank 9.

During normal operation of the transformer, the variations in temperature are within relatively narrow limits and the exchanges of air or gas between the overflow tank 7 and the atmosphere occur relatively infrequently. Also, exchanges of oil between the main and the overflow tanks are materially smaller than in the usual overflow tank structure. This latter result is secured by the arrangement whereby the pressure in the overflow tank opposes that of the main tank and a predetermined difference in pressure between the interior of the transformer tank and the atmosphere is necessary before the overflow tank is connected to the atmosphere by the valve 19. Accordingly, breathing is materially reduced during the norma] operation of the transformer.

A transformer constructedin accordance with my invention operates to maintain a body to inert'gas above the insulating oil that is substantially constant in quantity but the volume of which may vary slightly with the changes in pressure caused by variations in temperature. The de-oxidizing material to which the air or gas is exposed .deoxidizes the air initially within the tank and "removes such oxygen as may find its way into the space 7 from the oil, from leaks or from other sources. The deoxidizing apparatus maintains an inert gas in the overflow tank 7 9 and its associated parts in order that such oil as may enter the overflow tank is not oxidized and that, in case the oil level is below the entrance of pipe 10, no oxygen can enter the space 7.

The provision of deoxidizing apparatus of the character shown and described renders a transformer of the overflow ty e free from dangers of explosions resulting f i'om the formation of explosive mixtures of air and hydrocarbon gas. The oil is maintained at its highest dielectric strength by reason of the prevention not only of oxidation but of the absorption of air. Such gas as is absorbed by the oil is substantially pure nitrogen and its dielectric strengh is somewhat greater than that of oil under ordinary conditions.

A transformer of the character described above possesses the advantages that the inert gas space above the insulating oil is isolated from the atmosphere during normal operating conditions and the fact that a predetermined pressure is required before gas is expelled from, or air is admitted into, the tank reduces breathing to a minimum. The small amount of air taken into the main tank insures economy of the deoxidizing material.

avoided by placing the connection of the overflow tank slightly below the normal oil level and thereby limiting the degree of vacuum that may be produced.

While I have shown and described my invention as embodied within a transformer of the overflow type, it may be readily applied to transformers of the overflow type that are at present in operation by simple and obvious modification.

I claim as my invention:

1. The combination with a transformer having a tank partially filled with insulating fluid, of an auxiliary tank communicating with the transformer tank below the level of said fluid and deoxidizing means communicatincr with the space above the fluid in the transformer tank and with said auxiliary tank.

2. The combination with a transformerhaving a tank partially filled with insulating fluid, of an auxiliary tank communicating with the transformer tank below the level of said fluid and deoxidizing means communicating with the space above the fluid in the transformer tank, withsaid auxiliary tank and, also, under predetermined pressure con-' ditions, with the atmosphere.

3. The combination with a transformer having a tank partially filled with insulating fluid, of an auxiliary tank communicating with the transformer tank below the level of said fluid, deoxidizing apparatus communicating with the upper portion of said auxiliary tank and a valve for controlling the communicationof said deoxidizing apparatus with the atmosphere.

4. The combination with a main tank partially filled with insulating fluid and an auxiliary tank communicating with said main tank below the level of said fluid for receiving fluid from, and returning it to, said main tank upon corresponding changes in pressure therein whereby a substantially constant quantity of gas or air is maintained above said fluid, and valve-controlled means for connecting said auxiliary tank to the atmosphere under predetermined pressure conditions.

5. The combination with a main tank partially filled with insulating fluid and an auxiliary tank communicating with said maintank below the level of said fluid for receiving fluid from, and returning it to, said main tank upon corresponding changes in pressure therein whereby a substantially constant quantity of gas or air is maintained above said fluid, deoxidizing apparatus communieating with the space above the fluid in the main tank and with the upper portion of the auxiliary tank and a valve for controlling the connection of said apparatus to the atmosphere whereby gas may escape from said auxiliary tank and air may enter through said apparatus upon pressure conditions in said auxiliary tank.

6. The combination with a transformer having a tank partially filled with insulating fluid, of an auxiliary tank communicating with the transformer tank below the level of said fluid and means for supplying inert air or gas communicating with the space above the fluid in the transformer tank and with said auxiliary tank.

7. The combination with a transformer having a tank partially filled with insulating fluid, of an auxiliary tank communicating with the transformer tank below the level of said fluid, and means for supplying an inert gas or air communicating with the space above the fluid in the transformer tank, with said auxiliary tank and, also, under predetermined pressure conditions, with the atmoshere.

' 8. The combination with a casing partially filled with an insulating liquid medium, and electrical apparatus immersed in said liquid medium, of a chamber disposed above the level of said liquid medium and communicating with said casing below the level of said liquid medium, and a passage communicating with said chamber and traversed by .air from which oxygen has been largely excluded, said chamber, when said electrical apparatus is not in use, containing none of said liquid medium.

9. The combination with a casing partially filled with an insulating liquid medium and electrical apparatus immersed in said liquid medium, of a chamber disposed above the level of said liquid medium and communication with said casing below the level of said liquid medium, a valve-controlled passage open to the atmosphere and communicating with said chamber, and de-oxydizing material interposed in said passage, said chamber, when said'electrical apparatus is not in use, containing none of said liquid medium.

In testimony whereof, I have hereunto subscribed my name this 23rd day of August,

LELAND H. HILL. 

